Dry ice manufacture



4Filed .June 3b, 1949 Oct. 2, 95l w, H, Rupp 2,570,074

DRY ICE MQNUFACTURE 2 Sheets-Sheet l FEED V CO M i@ f 2 ,fao 19% ,..JJ' f 1- Y w r2 fir- WATEP.

H CONDENSE. -Lmf---gk '21 i2 L 1 I l iO 5J 5 VENT ma/T9 GJ ,SOLIDIFICATION J Y 'ZONE i5 i5 i VENT CQZ '.Dlzv ICE LM' Hopman` FI G l CJZter HfRupp :Im/enhor- Patented Oct. 2, 1951 DRY ICE MANUFACTURE Walter H. Rupp', Standard Oil ration o t Delaware Mountainside, N. J., assigner to Development Company, a corpo- Application June 30, 1949, Serial No. 102.270

13 Claims.

'I'he present invention is concerned with an improved process for the manufacture of carbon dioxide Dry Ice. The invention is more particularly concerned with a iiuidized process for the manufacture of Dry Ice spheres oi' predetermined and desired crystal size. In accordance with the present invention liquid carbon dioxide is flashed into a chamber and operating conditions adjusted so as to maintain the solid particles in the chamber a sutllcient length of time to secure crystals having the desired size. One specific adaptation oi' the present invention is to adjust the upiiowing gas velocities in the chamber suiliciently high to carry the snow crystals upwards Where theyv pass through cyclone lters and pilling machines to form spherical or cylindrical shapes. Another embodiment of the present invention is to so adjust operating conditions to remove carbon dioxide crystals of the desired size from the bottom of the chamber. A specic adaptation of the invention is to flash the liquid carbon dioxide into the bottom of a contacting zone under conditions that the upiiowing carbon dioxide countercurrently contacts a downilowing fine water spray or droplets of water. As the water descends carbon dioxide solidiiies on the surface of the water to form a solid coating of carbon dioxide Dry Ice, the thickness of which may be controlled by adjusting the time factor.

It is known in the art to manufacture carbon dioxide Dry Ice by various procedures. However, these procedures are generally directed toward the manufacture of relatively large pieces of Dry Ice. Under many conditions it is desirable to have relatively small spherical type pieces of carbon dioxide Dry Ice which may be readily handled as desired. By operating in accordance with the present p'rocess carbon dioxide Dry Ice of any desired dimension may be readily secured in a continuous manner.

The process of the present invention may be readily understood by reference to the drawings illustrating embodiments of the same. Figure 1 illustrates an adaptation of the invention wherein operating conditions employed are adjusted so as to remove carbon dioxide crystals of the desired size from the bottom of the chamber. A specific `embodiment illustrated in Figure 1 is to utilize a downflowing aqueous phase as a seeding medium. Figure 2 illustrates an vadaptation of the invention wherein the Dry Ice is removed overhead from the chamber and separated from carbon dioxide gas by means of cyclone separators or equivalent means.

Referring speclcally to Figure 1, purilied car- .fbon dioxide free of Water, oils, propane and sulfur compounds, as Well as other impurities, is introduced into the system by means of feed line I. The carbon dioxide is passed through a condensing zone 2 which is maintained under conditions adapted to condense the vaporous carbon dioxide. The liquid carbon dioxide is removed from zone 2 by means of line 3 and introduced into a vent zone 4. Uncondensed gases are removed overhead from zone 4 by means of line 5 while liquid carbon dioxide is removed by means of line 6. The liquid stream is passed through a pressure reducing valve 'I and flashed into the bottom of zone I Il by means of jets or similar means 9. Zone I Il is maintained throughoutvat a uniform temperature and pressure. The velocity ofthe upflowing gases is maintained within the range so as to secure carbon dioxide crystals of the desired size. As the size increases, the buoyancy of the crystals decreases, thus permitting the crystals to settle and be withdrawn from the bottom of chamber IIJ.

As indicated above, a particular embodiment of the invention as illustrated by Figure l is to introduce water in the form of a fine spray into the top of zone IIJ by means of line II and spray means I2. As the water flows down through zone III, carbon dioxide solidies on the surface of the water to form a solid coating of carbon dioxide ice. 'I'he solid carbon dioxide collects in the bottom of zone I0 and is removed by means of conduit I3 and passed into hopper I4. Carbon dioxide vapor is vented from zone I4 by means of line I5 While the dasired carbon dioxide product is removed from zone I4 by means of conduit or similar means I6.

Vaporous carbon dioxide is removed overhead from zone I0 by means of line I1, passed through heat exchange zone I 8, compressed in compression zone I9 and then preferably recycled to the system. This can be accomplished either by passing the gas into line I by means of line 20 or introducing the gas into line 6 by mans of line 2|. Line 6 may be used to control upiiowing gas velocity in zone I 0 and also can be used in conjunction with line 20 if desired.

Referring specifically to Figure 2, purified carbon dioxide gas is introduced into the system by means of line 40. The gas passes through a refrigeration zone 44 wherein the same is condensed. The condensed liquid is introduced into vent zone 42 by means of line 43. Uncondenshed gases may be withdrawn from zone 42 by means of line 4I'. Liquid carbon dioxide is withdrawn from the bottom of zone 42 by means of line 45 3 and flashed into zone 46. In accordance with this adaptation of the present invention the velocity of the uidizing gases together with the time of residence of the solid carbon dioxide crystals are so adjusted that crystals of the desired size are removed overhead from zone 46 by means of line 41 and introduced into cyclone separator or equivalent means 48. The crystals are removed from the bottom of the cyclone separator means 48 by means of line 49 and handled as desired.

(.aseous CO2 containing some small crystal sizes is removed from zone 48 by means of line -53 and preferably introduced into an electrical precipitation zone 54. Here gaseous CO2 is removed overhead while the small CO2 crystals are removed from the bottom of zone 54 and introduced into zone 50. The carbon dioxide removed overhead from zone 54 may be recycled to the system through compressor 55 and line 56. The recycled stream may be introduced into line 40, or into line 45 by means of line 51. The solid carbon dioxide precipitated in zone 54 is preferably introduced into pilling machine 50. The carbon dioxide spheres or cylinders' are withdrawn from zone 50 by means of line 5| and introduced into a carbon dioxide hopper 52. Under certain conditions it may be desirable to also introduce into zone 50, by means of line 65, at least a portion of the spheres withdrawn from zone 48 by means of line 49.

The feed carbon dioxide is obtainable from -several sources. For example, it may be obtained from certain carbon dioxide rich natural gases, or as a by-product of a fermentation process, or by the combustion of various gases, cokes or oil fuels, or by the decomposition of limestone. Obviously, it is essential that the nal Dry Ice product be of-an extremely high purity for the reason that Dry Ice often comes in direct contact with foodstuffs. Conseouently, it is generally essential to highly purify the carbon dioxide irrespective of the particular source of the CO2. It is also very desirable that the particle size of the solid CO2 be controllable in the manufacturing operation.

At the present time many complicated methods are utilized for the purification of CO2 in the Dry Ice industry. All of these methods, however, are characterized by the fact that the purification of the CO2 is carried out in gas phase. In general three steps are required to attain the necessary puriflcation. The first step may comprise the removal of sulfur compounds generally present in the impure carbon dioxide obtained from the sources mentioned. The sulfur compounds may be removed by a variety of chemical re- A agents. For example,.lead or zinc acetate solutions, sodium carbonate, sodium bicarbonate, caustic, diethanol amine, or other reagents may be employed. A second purification step is the removal of heavy oils and organic liquids and particularly of aromatic oils. Very small traces of heavy oils will impart unfavorable taste and odor to CO2, or to the Dry Ice formed from CO2.

i In order to effectively eliminate the heavy oils,

therefore, gaseous CO2 is conventionally contacted with charcoal, silica gel, etc. or alternatively the CO2 is carefully fractionated from the heavy oil. The third treating step conventionally required is the removal of excess water. It should be noted that it is not desirable to remove all water, since a small proportion is desirable in order to impart good crystalline structure to the Dry Ice formed. However, excess water is objectionable in tending to free control valves,

ill

heat exchangers and the like. Generally, solid drying agents are employed to remove undesired water from impure CO2 as for example alumina, fiorite, sulfuric acid, silica gel, as well as other agents.

The present invention is broadly concerned with a fluidized method for the manufacture of carbon` dioxide Dry Ice. This is accomplished by flashing liquid carbon dioxide into a flash zone. The flashing operation is accomplished by a relatively sharp reduction of the pressure maintained on the liquid carbon dioxide. In accordance with preferred embodiments of the process the liquid carbon dioxide is flashed into the bottom of a flashing zone whereby solid particles of carbon dioxide form. The. upflowing velocity of the carbon dioxide vapors is adjusted in a manner to maintain the mass of carbon dioxide solid particles in a relatively fluidized condition. In accordance with one embodiment of the process the relatively more buoyant particles are maintained in the flash zone until their size becomes such that they become less buoyant and tend to flow downwardly into the bottom of the flash zone. Thus, it is possible by this process to adjust the size of the solidparticles withdrawn from the bottom of the ash zone by controlling the velocity of the upflowing vapors. As the solid CO2 particles become larger, they become less buoyant and flow toward the bottom of the flash zone from where they may be collected and withdrawn. In accordance with this embodiment, a particularly desirable method of operation is to introduce a seeding medium, as for example, water into the top of the flash zone. The water is preferably introduced as a fine spray. The water sprayflows downwardly countercurrently into the upflowing CO2 vapors and acts as a seeding medium for the formation of solid carbon dioxide. Another embodiment of the process is to adjust the velocity of the upowing vapors so as to remove overhead from the flash zone the solidified carbon dioxide.

It is obvious that the specific operation conditions will depend upon various factors, as for example, the size of the particles desired, the size of the equipment utilized, and the quantity of product desired from any particular piece of equipment. However, in general, it is preferred that the liquid carbon dioxide prior to flashing the same be at a temperature in the range from about F. to 70 F. The pressure on the liquid stream is in the range from about 75 lbs. per sq. in. to 1000 lbs. per sq. in. absolute. Preferred temperatures are in the range from about. 0 to 40 F. and preferred pressures are in the range from about to 350 lbs. per sq. in. absolute. In accordance with the present invention, the flash chamber is maintained at about 15 to 300 lbs. absolute pressure and at a'temperature of about 0 to 109 F. Preferred flash chamber pressure is 20 lbs. absolute and 102 F. In general it is preferred that the temperature not vary more than 5 F. from the selected operating temperature and that the pressure not vary more than 5 lbs. per sq. in. from the operating pressure y selected. y

If water be employed, and if the operation is conducted so as to remove the product'from the bottom of the flash zone, the Water is introduced at a tempertaure in the range from about 35 F.l to 200 F. Particularly desirable results are secured when the temperature of the water introduced into the zone is in the range from about 50 SQ 60 The quantity of water introduced from about 2 ft. per second to 10 ft. per second.

Desirable velocities are in the range from 5 to 'I ft. per second.

When an operation is conducted wherein the solid particles are removed from the bottom of the flash zone, the velocityI should be adjusted to secure a segregation of the larger particles from the smaller particles, thus, as a particle becomes relatively larger the velocity of the upiiowing gas will not be suflicient to maintain the same in a fluidized state and it will fall to the bottom of the zone for collection and removal therefrom. A very desirable method of operating is to control the process so as to produce spheres having diameters in the range from Ve to 1/2 inch in diameter. 'Ihis is secured by having an ice residence time in the range from about 5minutes to 1 hour. The velocity under these conditions of the upfiowing gases is in the range from 0.5 ft. per second to 5.0 ft. per second. A desirable velocity is 1.0 to 3.0 ft. per second.

Having described the invention it is claimed:

1. Process for the manufacture of solid carbon dioxide which comprises introducing liquid carbon dioxide into a zone under conditions to vaporize the same, controlling conditions so as to solidify at least a portion of the CO: and maintaining said solidified C: in a iluidized state.

2. Process as defined by claim 1 wherein said solidified CO: is maintained in a iiuidized state by the uptlowing vaporous CO2.

3. Process as defined by claim 2 wherein. said solidified CO: is maintained in said zone a sumcient length of time to secure crystals of the desired size.

4. Process as dened by claim 3 wherein said solidified CO: is maintained in said zone for a residence time of from between 5 and 60 minutes whereby CO1 crystals having diameters in the range from Ve inch to t inch are secured.

5. Improved process for the manufacture of solid carbon dioxide which comprises maintaining a liquid stream of carbon dioxide under supcratmospheric pressure, introducing the liquid carbon dioxide into a flash zone and dashing the same by sharply reducing the pressure, whereby solid carbon dioxide forms, maintaining the solid carbon dioxide in a nuidized state by controlling the velocity of upflowing carbon dioxide Lapors. removing solid carbon dioxide from said ne.

6. Process as defined by claim 5 wherein the superatmospheric pressure is in the range from about to 1000 lbs. per sq. in. andV wherein the pressure in said flash zone is in the range from about 15 to 300 lbs. per sq. in.

7. Process as defined by claim 6 wherein said liquid stream is maintained at a temperature inv the range from about F. to 70 F. and wherein the temperature in said flash zone is in the range from about 0 F. to `109 F.

8. Improved process for the manufacture of solid carbon dioxide by a iluidiza'tion process which comprises introducing liquid carbon dioxide maintained at an elevated pressure into a iiash zone and flashing the same by sharply reducing the pressure thereon, maintaining the velocity of the upiiowing carbon dioxide gas in said zone so as to maintain the relatively smaller particles of carbon dioxide in the uidized state and to allow the relatively larger particles to settle to the bottom of said zone, withdrawing the larger particles from the bottom of said zone.

9. Process as defined by claim 8 wherein the velocity of the upilowing carbon dioxide gas is in the range from about 0.5 to 5 ft. per second.

10. Process as defined by claim 9 wherein a iine spray of water is introduced into the top of said flash zone.

11. Process as defined by claim 10 wherein the -amount of water introduced is in thee range from 0.1 to 1% by weight based upon the weight of CO2 introduced.

12. Process for the iluidization manufacture of solid carbon dioxide which comprises maintaining `a liquid stream of carbon dioxide under elevated pressures, introducing the same into a ilash zone and flashing the same by a sharp reduction of the pressure thereon, passing the carbon dioxide upwardly through said zone and withdrawing solid carbon dioxide overheadd'rom said zone, segregating vaporous carbon dioxide from solid sarbon dioxide.

13. Process as deiined by claim 12 wherein the velocity of the uptlowing gases is in the range of about2 to 10 ft. per second.

WALTER H.`RUPP.

REFERENCES CITED 'I'he following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,893,852 Sullivan Jan. 10, 1933 1,927,175 Josephson Sept. 19, 1933 2,011,550 Hasche Aug. 13, 1935 2,047,099 `July 7, 1936 2,464,089 Jones Mar. 8. 1949 

1. PROCESS FOR THE MANUFACTURE OF SOLID CARBON DIOXIDE WHICH COMPRISES INTRODUCING LIQUID CARBON DIOXIDE INTO A ZONE UNDER CONDITIONS SO AS TO SOLIDFY AT LEAST A PORTION OF THE CO2 AND MAINTAINING SAID SOLIDIFIED CO2 AND MAINTAINING SAID SOLIDIFIED CO2 IN A FLUIDIZED STATE. 